1. Field of the Invention
The present invention relates to a cold trap.
2. Description of the Related Art
There is a cold trap provided between a vacuum chamber and a vacuum pump, which is referred to as an in-line type cold trap. A cold panel is placed in an exhaust passage connecting an exhaust port of the vacuum chamber and an intake port of the vacuum pump. The vacuum pump may be a turbo molecular pump. When the in-line type cold trap is used in combination with the turbo molecular pump, the cold trap is primarily used to pump water vapor.
One of the methods to increase the pumping speed of a cold trap is to increase the area of the cold panel. However, such an attempt results in a portion of the exhaust passage being occupied by the cold panel and decrease in the cross-sectional area of the exhaust passage. Consequently, the conductance of the exhaust passage is decreased. This is particularly significant in the case of a thin cold trap having a planar cold panel such as a baffle or a perforated plate. If the conductance of the exhaust passage is decreased, the pumping speed of the downstream vacuum pump (e.g., turbo molecular pump) is decreased. In other words, a typical vacuum pumping system including the in-line type cold trap leads to a trade-off between the pumping speed of the cold trap and the pumping speed of the vacuum pump.